The present invention relates generally to the design of coolant filters which are used in the operation of motor vehicles, such as motor vehicles including a diesel engine. More specifically the present invention relates to the design of a coolant filter with a chemical additive disposed within the filter which is released into the circulating coolant. The chemical additive is referred to as a supplemental coolant additive or SCA and is used to maintain the desired amount of corrosion inhibitors in the coolant during engine operation.
The typical approach in the past was to change the coolant filter at the oil drain interval. This would normally be a two-month interval involving a mileage interval of between 15,000 and 20,000 miles. Under these conditions, a moderate amount of SCA could be introduced into the system and it would be able to maintain the desired level of corrosion inhibitors in the coolant. As the SCA is depleted and the coolant concentration of inhibitors decreases, it is likely time for a filter change and a new SCA charge is then available to be delivered to the circulating coolant when the new filter is installed.
Recently there has been an interest in dramatically extending the coolant service interval from the typical two months interval to a once-a-year interval. This in turn increases the interval mileage from 15,000-20,000 miles up to approximately 120,000 miles, or more. A coolant filter which is designed to be changed once a year contains a relatively large amount of SCA. For the most part, filters of conventional design add the SCA into the coolant during the first few hundred miles of operation. This fairly rapid addition (dissolving) of the SCA into the coolant is directly related to the creation of certain undesirable "side effects". These referenced side effects can create certain problems for the corresponding engine and should be avoided if possible.
One side effect to be avoided is coolant additive precipitation which in turn can cause water pump leakage. Another side effect is a less uniform level of liner pitting protection. By means of the present invention which involves a slow release mechanism for the SCA, the SCA is able to be added to the coolant slowly, over at least the first 25,000 miles of vehicle operation rather than all during the first few hundred miles of vehicle operation. The slow release of SCA helps to avoid coolant additive precipitation and in turn helps to avoid water pump leakage. The present invention also enables a more uniform level of liner pitting protection to be maintained.
Coolant filters of the type incorporating the present invention are relatively large and would contain approximately 1/2 pound of SCA as a fresh charge with a new filter. With earlier extended-interval filters, this 1/2 pound of SCA would all be introduced into the coolant in two to three hours of vehicle operation. When this much SCA hits the system all at once as a slug, it is slow to absorb because it is more than what the coolant can handle. As a result, the SCA is likely to come out of solution as a precipitate and collect as a solid. What can result from this are precipitate deposits on the water pump face seals. Since these face seals ride on each other at approximately 1800 RPM, a fairly warm environment is created during vehicle operation which can actually bake the chemical solids of the precipitated SCA onto the facing surfaces of the face seals. The build up of solids on the facing surfaces will cause leakage to occur which is an undesirable side effect of dumping the SCA into the coolant too rapidly.
One situation which complicates and exacerbates this particular side effect involves the specific chemical additives which are used in the SCA composition. These specific chemical additives include silicates and MBT. Since these chemical additives are not highly soluble, nor as soluble as other potential SCA additives which may have been previously used, there is an even greater tendency for these additives to either not go into solution or to precipitate out of solution. Thus, while the "slug" concentration which is being dumped into the coolant in such a short time is likely to precipitate out based solely on concentration, a less soluble additive contributes to the formation of a precipitate.
With regard to the side effect that relates to liner pitting protection, it should be understood that liner "pitting" is a special type of corrosion that results when the liners which are bathed in coolant vibrate. Since piston movement is not perfectly vertical, there is a slight rocking action or slap which creates the liner vibration. Vapor bubbles are created as the coolant is pulled away from the liner. These vapor bubbles implode and a type of shock wave hits the surface of the liner at points where vibration is the greatest. The problem with pitting is that if it continues, it can perforate the liner and admit coolant into the crankcase.
The SCA is helpful to reduce liner pitting by passivating the liner surface. The nitrites in the SCA form a tough oxide coating on the surface of the liner and if enough nitrite is present, pitting can be virtually eliminated. The preferred approach for creating and maintaining the tough oxide coating is to slowly release the SCA into the coolant over two to three months (approximately 25,000 miles). With the prior approach of rapidly dumping the SCA into the coolant, there will be a greater loss of SCA due to system leakage and thus less of the chemical is available for creating the tough oxide layer.
System leakage is a fairly common occurrence. Due to a variety of reasons which include loose hoses and system interface losses, the coolant system may loose between 1 and 2 gallons of coolant solution per month. If the SCA is added into the coolant rapidly, then the SCA unit volume concentration is greater than with a slow release. When the 1 to 2 gallons of coolant solution are lost, the amount of SCA which is lost is substantial. As a consequence, the SCA which is lost is never able to perform its intended function of passivating the liner. With a slow release of SCA, the loss due to leakage is more gradual and a majority of the SCA remains available for a longer period of time.
The design challenge which is addressed by the present invention is how to slowly release the SCA into the coolant. The present invention solves this design challenge in several ways, each of which is believed to provide a novel and unobvious solution.
Over the years a number of coolant filters have been designed, some of which incorporate a supplemental coolant additive, and the following listed patents are believed to provide a representative sampling of these earlier designs:
______________________________________ PATENT NO. PATENTEE ISSUE DATE ______________________________________ 5,435,346 Tregidgo et al. Jul. 25, 1995 5,395,518 Gulsvig Mar. 7, 1995 3,897,335 Brandt Jul. 29, 1975 3,369,666 Hultgren et al. Feb. 20, 1968 5,094,745 Reynolds Mar. 10, 1992 4,366,057 Bridges et al. Dec. 28, 1982 4,452,697 Conrad Jun. 5, 1984 4,782,891 Cheadle et al. Nov. 8, 1988 5,024,268 Cheadle et al. Jun. 18, 1981 5,114,575 Yano et al. May 19, 1992 5,209,842 Moor May 11, 1993 ______________________________________
In addition, the Penray Company of Wheeling, Ill. has offered for sale a "Need Release" filter which is intended to be an extended service interval coolant filter. With certain technical audiences this filter has been described as having a "delayed release" feature. The "Need Release" filter was originally offered by Nalco Chemical Company of Naperville, Ill. It is believed that the Nalco Chemical business has been acquired by the Penray Company. The "Need Release" filter includes a release mechanism which is based on magnesium corrosion. The filter has three large SCA pellets which are separated by magnesium plates all of which are housed in a copper sleeve or tube. Copper is used in order to establish a strong galvanic couple with the magnesium which promotes corrosion of the magnesium.
Other than operating on a different release principle and other than being structurally different from the claimed invention, the "Need Release" filter includes several drawbacks which are not present with the present invention. For example, the magnesium can dissolve into the coolant where it can cause additive precipitation and deposits in the cooling system. Another concern is that lube oil can on occasion leak into the coolant which will result in an oily film on the magnesium plate. This prevents the plate from corroding and releasing the SCA. The "Need Release" filter must be used with the proper HD type antifreeze and thus the product will not work properly when the coolant is only water. A further drawback is that the magnesium plate can build up a scale which stops corrosion which in turn prevents SCA release.
Although a variety of coolant filter designs have in the past been offered for sale and while extended service interval coolant filters are now receiving more attention, the present invention is novel and unobvious. The present invention provides a desirable solution to the design task which is directed to the avoidance of the undesirable side effects which have been described.